This invention relates to a method of producing an aliphatic polyester and to an aliphatic polyester obtained by the method.
Polyolefins and aromatic polyesters which are now used in a wide variety of fields have a problem because of their lack in biodegradability. While aliphatic polyesters which are biodegradable polymers are attractive, known aliphatic polyesters have a problem that physical properties thereof are not satisfactory and production thereof requires relatively high costs.
For example, polyhydroxybutyrate produced by using microorganisms requires high production costs. In addition, because a difference between the melting point and the decomposition point of polyhydroxybutyrate is small, the polyhydroxybutyrate is apt to be decomposed during molding to cause problems of generation of odor and reduction of mechanical properties. Polycaprolactone, which is one of a few currently industrially produced aliphatic polyesters, has a problem because the melting point is as low as about 60xc2x0 C. Polymers of hydroxycarboxylic acids, such as polylactic acid, have excellent biodegradability and are usable as topical absorbing material. However, they are only produced through complicated processes.
Aliphatic polyesters obtained by polycondensation of an aliphatic carboxylic acid compound (e.g. aliphatic carboxylic acid, ester or anhydride) and a glycol are known. Such polyesters, however, have a number average molecular weight of only several thousands and are ill-suited for the formation of films and fibers. Thus, methods have been proposed to increase the molecular weight of the aliphatic polyester by crosslinking with a diisocyanate or by using an additional comonomer such as a polyfunctional isocyanate. These methods, however, have a problem because a gel is apt to be formed or because additional process steps are required.
As an ester interchange catalyst for the production of aliphatic polyesters, titanium tetraisopropoxide is generally used. The known catalyst, however, is unsatisfactory with respect to the reaction rate of polyesterification and has an additional problem of coloring of the product. Furthermore, films or fibers prepared from the polyester have not satisfactory mechanical properties such as breaking elongation. With regard to the coloring of the polyester, U.S. Pat. No. 5,504,148 suggests the use of a phosphorus compound, particularly, polyphosphoric acid, as an anti-coloring agent. The use of phosphoric acid or polyphosphric acid, however, cannot sufficiently accelerate the polyesterification and, further, causes a problem of formation of by-products such as tetrahydrofuran derived from a diol.
It is, therefore, an object of the present invention to provide an industrially applicable method which can produce an aliphatic polyester having a resistance to hydrolysis.
Another object of the present invention is to provide a method which can produce an aliphatic polyester having good mechanical properties and good color tone at a high reaction rate.
It is a further object of the present invention to provide an aliphatic polyester obtained by the above method.
In accomplishing the foregoing objects, there is provided in accordance with the present invention a method of producing an aliphatic polyester, comprising polycondensing a raw material selected from the group consisting of
(A1) mixtures of an aliphatic diol and at least one aliphatic dicarboxylic acid compound selected from the group consisting of aliphatic dicarboxylic acids, diesters of aliphatic dicarboxylic acids and aliphatic dicarboxylic acid anhydrides,
(A2) prepolymers of mixtures (A1),
(A3) oxycarboxylic acid compounds,
(A4) prepolymers of oxycarboxylic acid compounds (A3),
(A5) mixtures of (a) an aliphatic diol, (b) at least one aliphatic dicarboxylic acid compound selected from the group consisting of aliphatic dicarboxylic acids, diesters of aliphatic dicarboxylic acids and aliphatic dicarboxylic acid anhydrides and (c) at least one auxiliary compound selected from the group consisting of aliphatic compounds and aromatic compounds having at least two functional groups which are reactive with at least one of (a) and (b),
(A6) prepolymers of mixtures (A5),
(A7) mixtures of (d) at least one oxycarboxylic acid compound and (e) at least one auxiliary compound other than oxycarboxylic acid compounds selected from the group consisting of aliphatic compounds and aromatic compounds having at least two functional groups which are reactive with (d), and
(A8) prepolymers of mixtures (A7) in the presence of a metal-containing ester interchange catalyst and a phosphorus-containing co-catalyst selected from the group consisting of
(B1) organic phosphinic acids,
(B2) monoammonium salts of hydrogen-containing phosphoric acids,
(B3) monoammonium salts of hydrogen-containing polyphosphoric acids,
(B4) calcium salts of hydrogen-containing phosphoric acids,
(B5) calcium salts of hydrogen-containing polyphosphoric acids,
(B6) magnesium salts of hydrogen-containing phosphoric acids,
(B7) magnesium salts of hydrogen-containing polyphosphoric acids, and
(B8) diarylphosphinic acids
Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments to follow.
A method of producing an aliphatic polyester according to the present invention includes a step of subjecting a raw material to polycondensation. The raw material is selected from the following substances (A1) through (A6).
Raw material (A1) is a mixture of an aliphatic diol and at least one aliphatic dicarboxylic acid compound selected from aliphatic dicarboxylic acids, diesters of aliphatic dicarboxylic acids and aliphatic dicarboxylic acid anhydrides. The aliphatic dicarboxylic acid compound may be represented by the following formula (1) or (2):
R11OOCxe2x80x94R1xe2x80x94COOR11xe2x80x83xe2x80x83(1) 
wherein R1 represents a divalent aliphatic group having 1-12 carbon atoms, preferably 1-10 carbon atoms, and R11 represents a hydrogen atom, a lower alkyl group or an aryl group.
The divalent aliphatic group R1 may be cyclic or linear and may be saturated or unsaturated. The divalent aliphatic group may contain a hetero atom such as oxygen. Illustrative of the divalent aliphatic groups are an alkylene group which may contain an ether linkage, an alkenylene group which may contain an ether linkage, an alkyleneoxy group and an oxyalkylene group. Specific examples of the divalent aliphatic groups include xe2x80x94CH2xe2x80x94, xe2x80x94C2H4xe2x80x94, xe2x80x94CH2Oxe2x80x94, xe2x80x94CH2OCH2xe2x80x94, xe2x80x94C3H6xe2x80x94, xe2x80x94C4H8xe2x80x94, xe2x80x94C6H12xe2x80x94, xe2x80x94C8H16xe2x80x94, xe2x80x94C12H24xe2x80x94 and xe2x80x94C12H22xe2x80x94.
The lower alkyl group R11 may have 1-6 carbon atoms, preferably 1-4 carbon atoms. The aryl group R11 may have 6-10 carbon atoms, preferably 6-8 carbon atoms, such as phenyl.
Illustrative of the aliphatic dicarboxylic acid compounds are succinic acid, adipic acid, sebacic acid, suberic acid, dodecanoic acid, diglycolic acid and acid anhydrides thereof.
The aliphatic diol to be used in conjunction with the above aliphatic dicarboxylic acid compounds may be represented by the following-formula (3):
HOxe2x80x94R2xe2x80x94OH
wherein R2 represents a divalent aliphatic group having 1-12 carbon atoms, preferably 2-10 carbon atoms, and R11 represents a hydrogen atom, a lower alkyl group or an aryl group.
The divalent aliphatic group R1 may be cyclic or linear and may be saturated or unsaturated. The divalent aliphatic group may contain a hetero atom such as oxygen. Illustrative of the divalent aliphatic groups are an alkylene group which may contain an ether linkage, an alkenylene group which may contain an ether linkage, an alkyleneoxy group and an oxyalkylene group. Specific examples of the divalent aliphatic groups include xe2x80x94CH2xe2x80x94, xe2x80x94C2H4xe2x80x94, xe2x80x94C3H6xe2x80x94, xe2x80x94C4H8xe2x80x94, xe2x80x94C6H12xe2x80x94, xe2x80x94C8H16xe2x80x94, xe2x80x94C12H24xe2x80x94, xe2x80x94C12H22xe2x80x94 (dodecenyl), xe2x80x94C6H10xe2x80x94 (cyclohexenyl), xe2x80x94CH2Oxe2x80x94 and xe2x80x94CH2OCH2xe2x80x94.
The aliphatic diol is generally used in an amount of 1-2 moles, preferably 1.02-1.6 moles, per mole of the carboxylic acid groups contained in the raw material (A1).
Raw material (A2) is a prepolymer of the above mixture (A1).
Raw material (A3) is an oxycarboxylic acid compound. The oxycarboxylic acid compound may be represented by the following formula (4) or (5):
HOxe2x80x94R3xe2x80x94COOR12xe2x80x83xe2x80x83(4) 
wherein R3 represents a divalent aliphatic group having 1-10 carbon atoms, preferably 2-8 carbon atoms, and R12 represents a hydrogen atom, a lower alkyl group or an aryl group.
Examples of the divalent aliphatic groups R3 in the formula (4) include those described above with regard to divalent aliphatic groups R1 and R2. The lower alkyl group R12 may have 1-6 carbon atoms, preferably 1-4 carbon atoms. The aryl group R12 may have 6-10 carbon atoms, preferably 6-8 carbon atoms, such as phenyl. Illustrative of suitable oxycarboxylic acids of the formula (4) are glycolic acid, lactic acid and buryric acid. The oxycarboxylic acid compound may be a cyclic diester (lactide) obtained by dehydration of two molecules of an oxycarboxylic acid such as glycolic acid or lactic acid.
Examples of the divalent aliphatic groups R3 (lactones) in the formula (5) include divalent, cyclic or linear aliphatic groups having 2-10 carbon atoms, preferably 2-5 carbon atoms. Illustrative of suitable lactones are caprolactone, valerolactone and laurolactone.
Raw material (A4) is a prepolymer of the above oxycarboxylic acid compound (A3).
Raw material (A5) is a mixture of (a) an aliphatic diol, (b) at least one aliphatic dicarboxylic acid compound selected from the group consisting of aliphatic dicarboxylic acids, diesters of aliphatic dicarboxylic acids and aliphatic dicarboxylic acid anhydrides and (c) at least one auxiliary compound selected from the group consisting of aliphatic compounds and aromatic compounds having at least two functional groups which are reactive with at least one of (a) and (b).
The aliphatic diol (a) may be the same as that described above with reference to the raw material (A1) and, thus, may be the compound of the formula (3). The aliphatic dicarboxylic acid compound (b) may be the same as that described above with reference the raw material (A1) and, thus, may be the compound of the formula (1) or (2).
The aliphatic diol (a) is generally used in an amount of 1-2 moles, preferably 1.02-1.6 moles, per mole of the carboxylic acid groups contained in the raw material (A5).
The auxiliary compound (c) is generally used in such an amount that the content of the auxiliary compound (c) in the aliphatic polyester is not greater than 50 mole %, preferably not greater than 40 mole % based on a total of the monomer components contained in the aliphatic polyester.
The auxiliary compound (c), namely an aliphatic or aromatic compound having at least two functional groups capable of reacting with at least one of the diol (a) and the aliphatic dicarboxylic acid compound (b) are preferably selected from oxycarboxylic acid compounds, carbonic acid esters, terephthalic acid compounds, polyhydric alcohols having at least three hydroxyl groups and polyoxyalkylene glycols.
The oxycarboxylic acid compounds as the auxiliary compound (c) may be the same as those described above with reference to the raw material (A3). The oxycarboxylic acid as the auxiliary compound (c) is generally used in such an amount that the content of the ester (oxycarboxylic acid ester) derived from the oxycarboxylic acid and contained in the aliphatic polyester is 2-50 mole %, preferably 5-40 mole %, based on a total of the ester components contained in the aliphatic polyester.
The carbonic acid ester as the auxiliary compound (c) may be a compound of the following formula (6):
R13OCOOR14xe2x80x83xe2x80x83(6)
wherein R13 and R14 independently represent a lower alkyl group or an aryl group. When both R13 and R14 are each a lower alkyl, the two lower alkyl groups may be bonded to each other to form a cyclic ester. The lower alkyl group R13, R14 may have 1-6 carbon atoms, preferably 1-4 carbon atoms. The aryl group R13, R14 may have 6-10 carbon atoms, preferably 6-8 carbon atoms, such as phenyl. The carbonic acid ester as the auxiliary compound (c) is generally used in such an amount that the content of the ester (carbonic acid ester) derived from the carbonic acid and contained in the aliphatic polyester is 2-50 mole %, preferably 5-40 mole %, based on a total of the ester components contained in the aliphatic polyester.
The terephthalic acid compound as the auxiliary compound (c) may be terephthalic acid, anhydride thereof or an ester thereof. The terephthalic acid compound as the auxiliary compound (c) is generally used in such an amount that the content of the ester (terephthalic acid ester) derived from the terephthalic acid compound and contained in the aliphatic polyester is 1-20 mole %, preferably 3-10 mole %, based on a total of the ester components contained in the aliphatic polyester.
The polyhydric alcohols having at least three hydroxyl groups as the auxiliary compound (c) may be, for example, glycerin, diglycerin, a polyglycerin compound, trimethylol propane or pentaerythritol. The number of the hydroxyl groups of the polyhydric alcohol is generally 3-6.
The polyhydric alcohol as the auxiliary compound (c) is generally used in such an amount that the content of the components derived from the polyhydric alcohol and contained in the aliphatic polyester is 0.01-0.5 mole %, preferably 0.1-0.3 mole %, based on a total of the ester components contained in the aliphatic polyester.
The polyglycerin compound may be a compound represented by the following formula (7):
HOxe2x80x94[C3H5(OR4)O]nxe2x80x94Hxe2x80x83xe2x80x83(7)
wherein R4 represents a hydrogen atom or an acyl group and n is an average polymerization degree which is generally 0.01-0.5, preferably 0.1-0.4. The acyl group may be represented by the following formula (8):
R15COxe2x80x94xe2x80x83xe2x80x83(8)
where R15 represents an aliphatic group having 1-20, preferably 1-6, carbon atoms, such as methyl, ethyl, propyl, butyl, hexyl, dodecyl and octadecyl. The polyglycerin compound as the auxiliary compound (c) is generally used in such an amount that the content of the ester (ether-containing ester) derived from the polyglycerin compound and contained in the aliphatic polyester is 0.01-0.5 mole %, preferably 0.1-0.4 mole %, based on a total of the ester components contained in the aliphatic polyester.
The polyoxyalkylene glycol as the auxiliary compound (c) may be a compound of the following formula (9)
HOxe2x80x94(AO)mxe2x80x94Hxe2x80x83xe2x80x83(9)
wherein AO represents an alkyleneoxy group having 2-4 carbon atoms, such as ethyleneoxy, propyleneoxy, butyleneoxy and mixtures thereof, and m is an average polymerization degree which is generally 2-10, preferably 2-5. The polyoxyalkylene glycol as the auxiliary compound (c) is generally used in such an amount that the content of the ester (polyoxyalkylene glycol ester) derived from the polyoxyalkylene glycol and contained in the aliphatic polyester is 0.1-50 mole %, preferably 1-40 mole %, based on a total of the ester components contained in the aliphatic polyester.
As the auxiliary compound (c), an oxypolybasic carboxylic acid such as malic acid, terephthalic acid or citric acid, a diisocyanate, a triol-type polypropylene glycol, an orthoformic acid ester or polyethylene terephthalate may also be used. The oxypolybasic carboxylic acid and polyhydric alcohol (e.g. trimethylol propane, pentaerythritol or glycerin), which serve to control biodegradability and other properties of the polyester, are generally used in such an amount that the content of the components derived therefrom and contained in the aliphatic polyester is 0.01-0.5 mole %, preferably 0.1-0.4 mole %, based on a total of the ester components contained in the aliphatic polyester. In the case of polyethylene terephthalate, the amount used is 1-20 mole %, preferably 1-10 mole %.
Glycolic acid or its ester is generally used in such an amount that the content of the ester units derived therefrom and contained in the aliphatic polyester is 0.0001-0.3 mole %, preferably 0.01-0.2 mole %, based on a total of the ester components contained in the aliphatic polyester.
The raw material (A6) is a prepolymer of a mixture (A5).
The raw material (A7) is a mixture of (d) at least one oxycarboxylic acid compound and (e) at least one auxiliary compound other than oxycarboxylic acid compounds and selected from the group consisting of aliphatic compounds and aromatic compounds having at least two functional groups which are reactive with (d).
The oxycarboxylic acid compound (d) may be the same as that described above with reference to the raw material (A3). The auxiliary compound (e) is preferably selected from carbonic acid esters, terephthalic acid compounds, polyhydric alcohols having at least three hydroxyl groups and polyoxyalkylene glycols. The carbonic acid esters, terephthalic acid compounds, polyhydric alcohols and polyoxyalkylene glycols may be the same as those described above with reference to the auxiliary compound (c). As the auxiliary compound (e), an oxypolybasic carboxylic acid such as malic acid, citric acid, diisocyanate, an orthoformic acid ester, phthalic acid, polyethylene terephthalate may also be used. The auxiliary compound (e) is generally used in such an amount that the content of the auxiliary compound (e) in the aliphatic polyester is not greater than 50 mole %, preferably not greater than 40 mole % based on a total of the monomer components contained in the aliphatic polyester.
The raw material (A8) is a prepolymer of a mixture (A7).
The polycondensation of the above raw material is carried out in the presence of a metal-containing ester interchange catalyst (esterification catalyst) and a phosphorus-containing co-catalyst.
The metal-containing ester interchange catalyst is a compound, such as an alcoholate, acetylacetonate chelate or acetate, of a metal such as an alkali metal (e.g. Li or K), an alkaline earth metal (e.g. Mg, Ca or Ba), a main group element (e.g. Sn, Bi, Sb or Ge), a transition element (e.g. Pb, Zn, Cd, Mn, Co, Ni, Zr, Ti Nb, or Fe) or a lanthanide metal (e.g. La, Sm, Eu, Er or Yb). Illustrative of suitable main group element-containing catalysts are dibutyl tin oxide, dibutyl tin laurate, antimony trioxide, germanium oxide, bismuth oxide carbonate and bismuth oxide acetate. Illustrative of suitable rare earth metal-containing catalysts are lanthanum acetate, samarium acetate, europium acetate, erbium acetate and ytterbium acetate. Illustrative of suitable transition element-containing catalysts are lead acetate, zinc acetate, zinc acetylacetonate, cadmium acetate, manganese acetate, manganese acetylacetonate, cobalt acetate, cobalt acetylacetonate, nickel acetate, nickel acetylacetonate, zirconium acetate, zirconium acetylacetonate, titanium acetate, tetrabutoxy titanate, tetraisopropoxy titanate, titanium oxyacetylacetonate, iron acetate, iron acetylacetonate and niobium acetate. The use of a transition element-containing catalyst is particularly preferred.
The above metal-containing ester interchange catalysts may be used singly or in combination. The catalyst is generally used in an amount of 10xe2x88x927 to 0.5 mole, preferably 0.005-0.3 mole, more preferably 0.01-0.15 mole, per 100 moles of the carboxyl group-containing compounds contained in the raw material for reasons of proper reaction rate and prevention of side reactions such as decomposition and crosslinking which cause coloring of the product.
The phosphorus-containing co-catalyst used in conjunction with the above metal-containing ester interchange catalyst is at least one compound selected from the following phosphorus compounds (B1)-(B8).
Co-catalyst (B1) is an organic phosphinic acid. The organic phosphinic acid may be represented by the following formula (10):
Oxe2x95x90P(OH)R2xe2x80x83xe2x80x83(10)
wherein R represents an aliphatic group or an aromatic group. The aliphatic group R may be linear or cyclic and have 1-12 carbon atoms, preferably 1-10 carbon atoms. The aromatic group R may be an aryl having 6-12 carbon atoms, preferably 6-10 carbon atoms or an aralkyl group having 7-12 carbon atoms, preferably 7-10 carbon atoms.
Illustrative of suitable organic phosphinic acids are phenylphosphinic acid, diphenylphosphinic acid, ditolylphosphinic acid, benzylphosphinic acid, methylphosphinic acid, n-butylphosphinic acid and cyclohexylphosphinic acid.
Co-catalyst (B2) is an monoammonium salt of hydrogen-containing phosphoric acid, such as ammonium dihydrogenphosphate.
Co-catalyst (B3) is a monoammonium salt of hydrogen-containing polyphosphoric acid.
Co-catalyst (B4) is a calcium salt of hydrogen-containing phosphoric acid, such as calcium phosphate dibasic or calcium dihydrogenphosphate.
Co-catalyst (B5) is a calcium salt of hydrogen-containing polyphosphoric acid.
Co-catalyst (B6) is a magnesium salt of hydrogen-containing phosphoric acid, such as magnesium phosphate dibasic or magnesium dihydrogenphosphate.
Co-catalyst (B7) is a magnesium salt of hydrogen-containing polyphosphoric acid.
The polyphosphates (B3), (B5) and (B7) had a degree of condensation (polymerization) of 2-10, preferably 2-6.
The co-catalyst is generally used in an amount providing an atomic ratio (P/M) of the phosphorus (P) of the co-catalyst to the metal (M) of said metal-containing ester interchange catalyst of 0.01-0.8, preferably 0.2-0.5.
By using the metal-containing catalyst in conjunction with the phosphorus-containing co-catalyst, aliphatic polyesters having a large molecular weight can be produced at a high reaction rate while preventing side reactions which result in the formation of tetrahydrofuran.
In one embodiment of the present invention, the raw material is heated in the presence of the metal-containing catalyst and the phosphorus-containing co-catalyst. It is preferred that the reaction be conducted while continuously removing water or a OH-containing compound such as methanol produced as a by-product. Thus, the reaction is preferably performed under conditions so that the water or OH-containing compound can be present as gas to expedite the removal thereof from the reaction system by distillation or by entrainment with a gaseous medium such as nitrogen gas. A reactor equipped with a distillation column is preferably used.
The reaction is generally performed at a temperature of 100-300xc2x0 C., preferably 120-250xc2x0 C., when methanol is produced as by-product. When by-product is water, the reaction is generally performed at a temperature of 130-300xc2x0 C., preferably 145-250xc2x0 C. The reaction may be performed at ambient pressure, a reduced pressure or under a pressurized condition. Ambient pressure or a reduced pressure is generally adopted.
To yield the aliphatic polyester efficiently, it is preferred that, when the reaction has proceeded to such a degree that about 90% of the calculated amount of the by-product (water or alcohol) has been obtained, the reaction conditions be changed by, for example, increasing the reaction temperature or by reducing the reaction pressure, so that polycondensation is accelerated with elimination of the aliphatic diol. Such reaction conditions are preferably such that the eliminated aliphatic diol can be present as gas.
In another embodiment, the polyester is produced by a two stage process including a first stage for the formation of prepolymers and a second stage for the polycondensation of the prepolymers.
In the first stage, the raw material is subjected to condensation in the presence of the metal-containing catalyst and the phosphorus-containing co-catalyst. The reaction temperature in the first stage is such that the by-product (water or alcohol) can be present as gas. The reaction pressure may be ambient pressure, a reduced pressure or an elevated pressure. Ambient pressure or a reduced pressure is generally adopted. The reaction is performed while removing the by-product. When the reaction has proceeded to such a degree that about 70-99% preferably 90-99%, of the calculated amount of the by-product (water or alcohol) has been obtained, the reaction temperature is increased and the reaction pressure is reduced. The first stage is generally carried out for 1-5 hours.
The thus formed reaction mixture containing oligomers are then polycondensed in the second stage. The metal-containing catalyst may be freshly added to the reaction mixture. In the second stage, aliphatic glycols bonded to termini of the oligomers are eliminated to obtain highly polycondensed polyesters having a weight average molecular weight of, for example, 80,000 or more. The reaction conditions in the second stage are such that the aliphatic glycol produced as by-product is present as gas. In the second stage, a higher reaction temperature and a lower reaction pressure are generally used than those in the first stage. The reaction pressure is preferably 0.005-5 Torr, more preferably 0.01-2 Torr. The reactor used for the second stage may be the same as that used in the first stage or may have an improved stirring efficiency as compared with that used in the first stage. The reaction time is generally 1.5-10 hours.
The phosphorus-containing co-catalyst is preferably added before commencement of the first stage but, if desired, may be added before start of the second stage.
In one embodiment, the polyester of the present invention contains ether-containing ester components of the formula (11) shown below and 1-30 mole %, preferably 5-20 mole %, of oxycarboxylic acid ester components of the formula (12) shown below and/or 1-30 mole %, preferably 5-20 mole %, of carbonic acid ester components of the formula (13) shown below:
(xe2x80x94COxe2x80x94R1xe2x80x94COxe2x80x94Oxe2x80x94R2xe2x80x94Oxe2x80x94)xe2x80x83xe2x80x83(11)
(xe2x80x94COxe2x80x94R3xe2x80x94Oxe2x80x94)xe2x80x83xe2x80x83(12)
(xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94)xe2x80x83xe2x80x83(13)
wherein R1, R2 and R3 are as defined previously.
In another embodiment, the polyester of the present invention contains oxycarboxylic acid ester components of the formula (14) shown below and 1-50 mole %, preferably 5-40 mole %, of carbonic acid ester components of the formula (15) shown below:
(xe2x80x94COxe2x80x94R3xe2x80x94Oxe2x80x94)xe2x80x83xe2x80x83(14)
(xe2x80x94Oxe2x80x94COxe2x80x94Oxe2x80x94)xe2x80x83xe2x80x83(15)
wherein R3 is as defined previously.
In a further embodiment, the polyester of the present invention contains dicarboxylic acid ester components of the formula (16) shown below and 0.1-50 mole %, preferably 0.5-40 mole %, of ether containing ester components of the formula (17) shown below:
(xe2x80x94COxe2x80x94R1xe2x80x94COxe2x80x94Oxe2x80x94R2xe2x80x94Oxe2x80x94)xe2x80x83xe2x80x83(16)
(xe2x80x94COxe2x80x94R1xe2x80x94COxe2x80x94Oxe2x80x94R4xe2x80x94Oxe2x80x94)xe2x80x83xe2x80x83(17)
wherein R4 represents an ether group-containing divalent aliphatic group having 4-12 carbon atoms.
In yet a further embodiment, the polyester of the present invention contains terephthalic acid ester components of the formula (18) shown below in an amount of 0.1-20 mole %, preferably 0.5-10 mole %.
(xe2x80x94COxe2x80x94C6H4xe2x80x94COxe2x80x94)xe2x80x83xe2x80x83(18)
The aliphatic polyester obtained by the method of the present invention preferably has a weight average molecular weight of 80,000 or more and is substantially linear. The upper limit of the weight average molecular weight is generally about 300,000. The polyester is biodegradable in nature and permits recovery of the raw materials by alcoholysis or hydrolysis. The catalyst and co-catalyst may be separated from the polyester, if desired. Since the amount of the catalyst and co-catalyst is small, the separation thereof may be omitted to save costs.
The following examples will further illustrate the present invention. The molecular weight and molecular weight distribution of polyesters are measured by gel permeation chromatography (GPC) using chloroform as an eluent and polystyrene as a standard. The melting point and glass transition point of polyesters are measured with a differential scanning calorimeter (DSC), while the thermal decomposition temperature is measured with a thermogravimetric analyzer (TG). Breaking elongation is measured at 25xc2x0 C. at a drawing rate of 10 mm per minute with a sample having a thickness of 0.25 mm (Japanese Industrial Standard JIS K7127, sample type 5).